As a means for reducing vibration or noise which machinery produces, an active vibration control apparatus and an active noise control apparatus are known. Since the present invention is applicable to both of them, the instant specification refers to them as an active vibration/noise control apparatus collectively which means an “apparatus for controlling vibration or noise”. Likewise, as for “vibration or noise” of machinery, they are referred to as vibration/noise collectively.
A conventional active vibration/noise control apparatus detects vibration or noise, which is a controlled subject, with a detector such as a vibration sensor or microphone, and controls it by outputting the same amplitude and anti-phase control signal for cancellation. As an example of such an active vibration/noise control apparatus, Patent Document 1, for example, discloses an active noise/vibration control apparatus that uses an adaptive notch filter. Here, if disturbance unrelated to the controlled subject is provided to the detector, the apparatus responds to it, and offers a problem of deviating the amplitude and phase of the control signal, thereby reducing suppression effect, or a problem of the apparatus itself of producing extraordinary vibration or a strange sound. As a concrete example of such disturbance, there is an impact or the sound of the impact caused by contact of a person or object with the vibration sensor, microphone or the body of the apparatus, or external sounds unrelated to the vibration/noise such as human voices input to the microphone.
Regarding such a problem, Patent Document 2, for example, discloses a method which decides, if the amplitude and the rate of change of the amplitude of the noise signal detected with the detector exceed a prescribed threshold, that it is an extraordinary input, that is, the disturbance, and suppresses the change of the control signal.